With such actuating mechanisms there is the problem that only a limited swivelling angle is available for the swivelling path of the actuating lever. This swivelling angle cannot be increased resulting consequences for operating quality. In this connection, it proves to be a disadvantage that the available swivelling range, already limited, anyway, which determines the actuating course of the safety-catch, cannot be fully utilized. The ability to utilize the swivelling angle is reduced because the seat back cannot be folded into the forward position from a preset fixed position, but rather the folding procedure must be possible with every one of the leaning settings conceivable for use. In actuality, a swivelling path of 40.degree., as an example, is reduced by 10.degree., for example, because the seat-back angle adjustable with an angle adjusting mechanism can easily vary by 60.degree. or more in the state of use.